1. Field of the Invention
At least one embodiment of the invention applies to the field of medical engineering and relate to a medical sensor system comprising a sensor lead which can be implanted in the body of a human or an animal and comprises one or more sensors for detecting biological measured quantities.
2. Description of the Related Art
The contraction of the heart is based on electrical stimulation that is generated in the sinoatrial node in the normal case, and is transmitted by the heart's natural conducting system to the cardiac muscle cells. The voltage changes that occur as a result can be measured on the surface of the body using electrodes, thereby enabling findings regarding the state and diseases of the heart to be obtained on the basis of the variation over time (ECG=electrocardiogram). For instance, the electrocardiogram can be used to detect cardiac arrhythmias, for instance, in particular tachycardias and bradycardias, and ventricular extrasystoles.
Cardiac arrhythmias often do not occur during an examination in a medical office or in the hospital, but rather in certain situations, such as during physical exertion or during the night. It is common practice to attach a wearable ECG recorder to patients for recording a so-called long-term ECG for a period of 24 hours or longer, for instance. Electrodes connected to the ECG recorder are adhered to the patient's chest and record the electrical signals. This is uncomfortable to the patient, since the adhered electrodes interfere with personal hygiene, and the ECG recorder is usually visible as it is carried on the body. In addition, the adhered electrodes can easily become detached, and so such a wearable ECG recorder is not suitable for use to perform an extended observation of the electrical signals of the heart, e.g. for a period of several weeks, months, or years.
ECG recorders that can be implanted in the patient's body are known in medical practice. In that particular case, an ECG recorder in the form of a fully encapsulated implant is implanted in the patient to be monitored, in an implant pocket subcutaneously or submuscularly close to the heart. The implant is typically equipped with a telemetry interface via which information can be requested. A disadvantage of implantable ECG recorders is the fact that implantation is relatively complex, and the implant pocket must be opened as soon as diagnostics have been completed or the implant battery is exhausted. This is difficult for the patient, leaves a relatively large scar, and is associated with a significant risk of infection due to the implant pocket. A further disadvantage involves the relatively large dimensions of the implant, which are determined mainly by the battery size, which depends on the service life, the size of the antenna for the telemetry interface, and the biocompatible encapsulation of the implant. Implants are therefore usually relatively large in practical application. As a result, the implants are not adapted with the primary aim of obtaining an optimal ECG reading, nor can they always be placed in the most favorable location with respect to the ECG reading, due to specific anatomical circumstances, thereby possibly resulting in poorer quality diagnostics. A further disadvantage is posed by the relatively high costs of such an implantable ECG recorder, since all components must meet the demands of an implantable medical device, the battery must be designed large enough to prevent the need to remove it prematurely, and a relatively expensive telemetry interface must be provided. Moreover, acceptance problems arise with young patients in particular, since such an implant wears out, and, as mentioned above, the implantation leaves a relatively large scar. In addition, the implant can present a contraindication for certain diagnostic and therapeutic procedures (e.g. a nuclear resonance tomographic examination).